<!DOCTYPE html>
<html>
<head>
	<title></title>
	<style type="text/css">

.demo {
	width: 300px;
	height: 300px;
	left: 30px;
	background: #342;
	position: static;
}	
.main {
	width: 300px;
	height: 300px;
	left: 30px;
	background: #342;
	position: relative;
}
.son {
	width: 300px;
	height: 300px;
	left: 20px;
	background: #666;
	position: absolute;
}
.fix {
	width: 300px;
	height: 300px;
	left: 20px;
	background: #666;
	position: fixed;
}
	</style>
}
</head>
<body>
<div class="demo"></div>
<div class="main">
	<div class="son"></div>
</div>
<div class="fix"></div>


</body>
</html>